This invention relates to moldable plastic wafer baskets or carriers for silicon wafers which are designed for carrying and storing silicon wafers used in the production of integrated circuit chips.
The processing of wafers requires that they be successively immersed or sprayed with liquids and gases. Some of the chemical baths include various corrosive chemicals while certain of the baths are extremely hot, in the range of 180.degree. C. Wafers that are presently being processed have diameters as large as 8 inches. Typically, 25 of such wafers are within a single wafer basket or carrier which requires that a carrier be large enough for this capacity. Such a carrier which is full of wafers will weigh eight to ten pounds. Ten inch wafers are now starting to be used and will be in common use in the foreseeable future.
Accordingly, the wafer carriers used to hold the silicon wafers during processing are formed of moldable plastic which preferably is inert and highly resistent to the corrosive effect of chemicals used, and highly resistive to the high bath temperatures regularly employed during the processing. Conventionally, the molded plastic used in carriers is PFA Teflon.RTM.(a registered trademark of E. I. du Pont de Nemours Company), a perfluoroalkoxy-substituted polytetrafluoroethylene resin. For less harsh environments and for wafer storage and shipping, carriers have been made of polypropylene.
It should be recognized that the silicon wafers are extremely delicate and brittle and may be only a few thousandths of an inch thick. The silicon wafers are extremely valuable and breakage of a wafer may represent a significant loss. Particulate and other contamination of wafers must also be avoided in order to manufacture integrated circuit chips operable within the range of standards set by the industry. Thus, there has been an increase in automated handling away from manual handling of the silicon wafers and carriers. Robotic arms are increasingly being utilized for handling both the wafer carrier and the individual silicon wafers where possible.
Automated handling of silicon wafers and wafer carriers require that the envelope of space within a carrier wherein a particular silicon wafer is to be located must be maintained within close tolerances. This is necessary to avoid wafer breakage. Problems have been encountered in handling these large but thin silicon wafers because the wafer carriers have been known to soften and distort when exposed to 180.degree. C. temperatures. Also, warping of the wafer carriers during their cooling down period after injection molding has also been known to occur. Such warping, distorting and bowing of the wafer carriers tends to put added compressive pressure on the edges of the delicate wafers. Therefore, a moldable plastic, distortion and warp resistent wafer carrier is highly desirable for processing, carrying and storing silicon wafers.